Spectroscopic characterization of 1,5-diphenyl-3,7-dihydroxy-1,5-diazacyclooctane — (8C ring compound) formed in N,N-diglycidylanaline/aniline curing systems

Summary A NMR and infrared analysis of the cyclic product formed by the reaction of N,N-diglycidylaniline with aniline confirms the structure of an eight-membered ring (I). The conformational structure of this compound is discussed.     

The crystal structure of the processive endocellulase CelF of Clostridium cellulolyticum in complex with a thiooligosaccharide inhibitor at 2.0 A resolution

The mesophilic bacterium Clostridium cellulolyticum exports multienzyme complexes called cellulosomes to digest cellulose. One of the three major components of the cellulosome is the processive endocellulase CelF. The crystal structure of the catalytic domain of CelF in complex with two molecules of a thiooligosaccharide inhibitor was determined at 2.0 A resolution. This is the first three-dimensional structure to be solved of a member of the family 48 glycosyl hydrolases. The structure consists of an (alpha alpha)6-helix barrel with long loops on the N-terminal side of the inner helices, which form a tunnel, and an open cleft region covering one side of the barrel. One inhibitor molecule is enclosed in the tunnel, the other exposed in the open cleft. The active centre is located in a depression at the junction of the cleft and tunnel regions. Glu55 is the proposed proton donor in the cleavage reaction, while the corresponding base is proposed to be either Glu44 or Asp230. The orientation of the reducing ends of the inhibitor molecules together with the chain translation through the tunnel in the direction of the active centre indicates that CelF cleaves processively cellobiose from the reducing to the non-reducing end of the cellulose chain.     

Fracture behaviour of single crystal silicon microstructures

The fracture behaviour of single crystal silicon (SCSi) microstructures is analysed based on microme-chanical torsional and tensile experiments. The uniaxial testpieces are characterised by the presence of sharp not-ches at the gauge length extremities. The critical loading conditions are reproduced in a finite element model in order to identify the analogies of the failure conditions in tension and torsion. The stress field in the vicinity of the notch tip (were cracks originate) is analyzed, and fracture mechanics parameters are determined. In the finite element model a crack, reproducing the failure process observed in the experiments, is included. The crack area is incrementally increased and the energy release rate for the critical loading conditions in tension and torsion is calculated. Based on these results a failure criterion is formulated along with a procedure for the mechanical integrity analysis of SCSi microstructures of arbitrary shape and loading conditions.     

Membrane automata with priorities

In this paper the one-way P automata with priorities are introduced. Such automata are P systems where the membranes are only allowed to consume objects from parent membranes, under the given conditions. The result of computation of these systems is the set of multiset sequences consumed by skin membrane into the system. The rules associated in some order with each membrane cannot modify any objects, they can only move them through membrane. We show that P automata with priorities and two membranes can accept every recursively enumerated language.     

Finite element program for moisture and heat transfer in heated concrete

A new axisymmetric finite element program for the analysis of pore pressure, moisture content and temperature in heated concrete is described. The program is based on the diffusion equations for coupled heat and moisture transfer and uses a step-by-step time integration. The finite element scheme is based on Galerkin method. For time integration a step-by-step solution with iterations is used. The numerical analysis is complicated by the fact that the sorption isotherms exhibit a steep jump at saturation-nonsaturation transitions, and that the permeability dependence on temperature exhibits a jump of two orders of magnitude at 100°C. The mathematical model takes into account the release of chemically bound water due to dehydration and the associated changes in the pore space. The program may also be used at normal temperatures. Predictions of the program are compared with tests by HEDL as well as two other existing programs.     

Quasicrystal–crystal structural transformation in Al–5 wt.% Mn alloy

The atomic structure of Al–5 wt.%Mn (Al–5Mn) alloy, prepared by rapid solidification, and pre-annealed at 623 and 773 K for 5 and 1 h, respectively, were characterized by X-ray powder diffraction (XRD) and extended X-ray absorption fine structure (XAFS) techniques. The sample in as-quenched stage was found crystalline, consisting of metastable α-Al (Al–Mn solid solution) and icosahedral quasicrystalline I-Al₆Mn phases. Five hours annealing at 623 K proved thermal stability of both the phases. Pre-annealing at 773 K/1 h on the other hand leads to α-Al phase decomposition and structural transformation of metastable I-Al₆Mn to stable orthorhombic Al₆Mn phase. The EXAFS results indicate that Mn atoms are located preferably on the outer shell of icosahedrons. During the I-Al₆Mn→o-Al₆Mn transformation the total Al atoms coordinating one Mn were found to be constant (∼10). Based on the results, only distance/symmetry changes in atomic arrangement around Mn atoms were suggested.     

Evaluation of applicability of 2D iron core model for two-limb configuration of GOLEM tokamak

This paper presents evaluation of applicability of 2D iron core model for highly non-axisymmetric two limb configuration of GOLEM tokamak (former CASTOR). Presented results explain the long-term discrepancy between measured magnitudes of external poloidal field and those calculated by air-core approach on this tokamak. The model has been applied to two poloidal planes at different toroidal angles in the vacuum vessel region and has shown that close to central column of the transformer, it is possible to correct for 3D effects by variation of chosen dimensions of axisymmetric iron core model. Satisfactory agreement of the 2D model results with the measured distribution of B_R field component was achieved.     

Compound Size Effect in Composite Beams with Softening Connectors.?I: Energy Approach

The size effect on the nominal strength of steel-concrete composite beams caused by shear failures of connectors such as welded studs is analyzed by two different approaches: (1) In this paper (Part I) by a fracture type analysis of the energy release caused by propagation of the zone of failed connectors along the beam; and (2) in a companion paper (Part II) by a direct solution of the load-deflection diagrams from the differential equations of beam bending theory. The former can capture the large size asymptotic size effect and yields simple formulas suitable for design, whereas the latter can provide the solution for small beam sizes for which the connector failure zone is not much shorter than the span. The force-slip diagram of the connectors exhibits postpeak softening, which engenders an energetic size effect on the nominal strength of the connector. If the connectors are geometrically scaled with the beam, the size effect in the shear failure of connectors (mesoscale) is superimposed on the size effect due to propagation of the zone of connector failures along the beam (macroscale), producing in the beam as a whole a compound size effect that is stronger than in linear elastic failure mechanics. If the connector sizes and the interface area per connector are not scaled with the overall dimensions of the composite beam, the size effect law proposed by Ba?ant in 1984 is applicable. Comparisons with available test results are presented in Part II.